1. Field of the Disclosure
The present disclosure relates generally to an apparatus and a method for selecting an antenna for a cell search in a wireless terminal.
2. Description of the Related Art
In order to meet wireless traffic demands, which have increased since deployment of 4th-generation (4G) communication systems, efforts have been made to develop an improved 5th-generation (5G) or pre-5G communication system. The 5G or pre-5G communication system is also referred to as a “Beyond 4G Network” communication system or a “Post LTE” system.
The 5G communication system is implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of radio waves and increase transmission distance in the higher frequency bands, beamforming, massive multiple-input multiple-output (MIMO), full dimensional MIMO (FD-MIMO), an array antenna, analog beamforming, and large scale antenna techniques have been developed in 5G communication systems.
In addition, in 5G communication systems, technological development for system network improvement is under way based on advanced small cells, cloud radio access networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving networks, cooperative communication, coordinated multi-points (CoMP), reception-end interference cancellation, and the like.
Also in a 5G system, hybrid frequency shift keying (FSK) and quadrature amplitude modulation (QAM) (FQAM) and sliding window superposition coding (SWSC) have been developed as advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) have been developed as an advanced access technology.
Generally, a wireless terminal needs to search for a cell to initially access in a network, or for synchronization with an adjacent cell (also referred to as a “neighboring cell”) to support mobility and to measure reception quality. The wireless terminal determines a target cell to attempt to initially access by evaluating the reception quality, or determines whether to perform a handover or cell reselection by evaluating the reception quality of a current cell (also referred to as a “serving cell”) and the reception quality of at least one neighboring cell. For example, handover may be performed by the wireless terminal in a mode RRC_CONNECTED (e.g., an active state), and the cell reselection may be performed by the wireless terminal in a mode RRC_IDLE (e.g., an idle state).
When determining the target cell to attempt to initially access, or when measuring the reception quality for handover or cell reselection, a wireless terminal using a single antenna does not require antenna selection. However, for a wireless terminal using multiple antennas, an antenna to be used for measurement of the reception quality may be an important factor in determining communication quality.
For example, for a wireless terminal supporting reception (Rx) diversity based on multiple antennas in a good wireless communication environment, such as a strong electric-field environment, antenna selection may have minimal effect on communication quality. That is, when the wireless terminal uses the multiple antennas, a procedure for antenna selection may not be required in the strong electric-field environment.
However, for a wireless terminal supporting Rx diversity based on multiple antennas in a poor wireless communication environment, such as a weak electric-field environment, antenna selection may have a great impact on communication quality. That is, when the wireless terminal uses the multiple antennas, success or failure of a cell search may depend on a selected antenna in the weak electric-field environment. For example, a wireless terminal having two antennas may fail in a cell search with a second antenna despite succeeding in a cell search with a first antenna when reception quality in a particular cell is measured as good by the first antenna and is measured as poor by the second antenna.
To solve this problem, in the weak electric-field environment, all paths that may be obtained in the multiple antennas may be activated and a search may be performed corresponding to each of the paths, thus improving search performance. In this case, however, time and power consumed for the search may increase.